1. Field of the Invention
The present invention relates to a process and an apparatus for manufacturing a reinforcing structure for tyres of vehicles through application of strip-like elements in mutual side by side relationship along the circumferential extension of a toroidal support so as to form at least one reinforcing layer having a continuous circumferential extension around a geometric rotation axis.
2. Description of the Related Art
Each of said strip-like elements comprises longitudinal reinforcing threadlike elements disposed parallel to each other and at least partly coated with at least one layer of elastomeric material.
In the present specification, the invention will be depicted with particular reference to manufacture of a belt structure of a tyre. It is however pointed out already now that the apparatus in accordance with the invention can be also used for manufacturing a carcass structure of the tyre or, more generally, any other reinforcing structure comprising cords oriented parallel to each other and according to a predetermined angle relative to an equatorial plane of the tyre itself.
A tyre for vehicle wheels usually comprises a carcass structure essentially made up of one or more carcass plies of a substantially toroidal shape and having their axially opposite side edges in engagement with respective annular reinforcing structures incorporating circular inserts usually referred to as “bead cores”. Each annular reinforcing structure is incorporated into a so-called “bead” defined along an inner circumferential edge of the tyre for anchoring of the latter to a corresponding mounting rim.
Applied to the carcass structure, at a radially external position, is a belt structure comprising one or more belt layers in the form of an endless ring and essentially made up of textile or metallic cords suitably oriented with respect to each other and to the cords belonging to the adjacent carcass plies.
Also applied to the belt structure, at a radially external position, is a tread band usually consisting of a strip of elastomeric material of suitable thickness. It is to be pointed out that, to the aims of the present description, by the term “elastomeric material” it is intended a compound comprising at least one elastomeric polymer and at least one reinforcing filler. Preferably, this compound further comprises additives such as cross-linking agents and/or plasticizers, for example. Due to the presence of the cross-linking agents, this material can be cross-linked through heating, so as to form the final article of manufacture.
A pair of sidewalls is applied to the opposite sides of the tyre, each of them coating a side portion of the tyre included between a so-called shoulder region, located close to the corresponding side edge of the tread band, and the corresponding bead.
Recently, particular attention has been paid to the possibility of finding production methods enabling manufacture of intermediate semi-finished products to be eliminated or at least reduced, in the field of tyre building. For instance, in the European Patent Application EP09288680 in the name of the same Applicant, it is described a method of manufacturing tyres in which the carcass ply or plies, as well as each of the belt layers, are obtained by laying a plurality of strip-like elements one after the other in circumferential side by side relationship, on a toroidal support conforming in shape to the inner conformation of the tyre to be obtained.
In document U.S. Pat. No. 6,355,126 it is described a method and an apparatus for manufacturing a belt layer through laying of strip-like elements cut from a continuous ribbon-like element. Each strip-like element, once cut from the continuous ribbon-like element, is picked up by grip members of the magnetic type or provided with suction cups, controlled by one or more robotized arms. The grip members retain the strip-like element at the opposite ends of same, and possibly at a central portion thereof, and are moved upon command of the robotized arms to cause application of the strip-like element itself onto the outer surface of a toroidal support, according to a predetermined angle relative to the circumferential extension of said support. When application has been completed, the toroidal support is rotated around its geometric axis according to a predetermined angle, to enable application of a new strip-like segment at a position adjacent to the previously applied one. Sequential repetition of the above described steps causes formation of a belt layer extending along the whole circumferential extension of the toroidal support.
In document WO01/38077 in the name of the same Applicant it is described another method and apparatus for manufacturing a belt layer for vehicle tyres, through laying of strip-like elements cut from a continuous ribbon-like element. In detail, the strip-like segments thus cut are applied in mutual side by side relationship along the circumferential extension of a toroidal support to form at least one reinforcing layer having a continuous circumferential extension around a geometric rotation axis (X-X) of the toroidal support. During this application, a relative angular rotation is determined between the strip-like segment itself and the toroidal support, around a correction axis substantially radial to the geometric rotation axis of the toroidal support.
The Applicant has however perceived that laying of strip-like elements carried out following the teachings of the known art could determine unevenness in the reinforcing structure.
In particular, the Applicant has noticed that in the laying apparatus according to application WO01/38077 it is difficult to carefully control laying of the ends of the strip-like element. This could involve a loss of accuracy in following the predetermined laying trajectory and an insufficient adhesion of the end tips of the strip-like element.
The Applicant has further noticed that in laying apparatus for strip-like elements of the known art it is not possible to maintain a contact between the element exerting a laying pressure and the supporting drum, over the whole width of the presser element along all the laying outline, above all with high-camber outlines of the toroidal support, such as the toroidal supports used for motorcycle tyres for example.
This lack of contact may cause, in this case too, an insufficient adhesion of the strip-like element, above all at the ends thereof.